After the growing phase is complete, cannabis plants are harvested by trimming off branches that include a long, central stem, large “fan” leaves (also called water leaves), and a cola (also called a bud or flower), in which numerous smaller leaves (called sugar leaves) are also interspersed. The next step in the harvest process is the removal of fan leaves and sugar leaves, either before or during the drying process, so that what is left are the parts of the plant—the buds or flowers, including trichomes (see below)—containing a higher concentration of active compounds, primarily tetrahydrocannabinol (THC), cannabidiol (CBD) and numerous other cannabinoids. These active compounds are particularly concentrated in the flower and in the nearly microscopic, translucent resin glands on the flower surface called trichomes. The trichomes and the flower are delicate structures and easily damaged or broken through handling. Thus, one objective of the trimming process is to remove as many of the low-cannabinoid leaves as possible without damaging or removing the high-cannabinoid flower and trichomes.
The trimming process has been traditionally accomplished using manual labor, in which an individual uses a pair of small scissors to cut away the fan leaves, sugar leaves and other low-cannabinoid parts of the plant. Manual trimming, however, is slow, monotonous, imprecise, expensive and exposes valuable (and otherwise tightly controlled) inventories of cannabis flowers to theft by workers and damage in the trimming process.
In response to these drawbacks (including but not limited to damage to trichomes, tedious manual labor, damage to the product, reduction in product margins and shrinkage through theft), various mechanical devices have been created to trim harvested plants, including the TRIMPRO Rotor XL (www.trimpro.com), the CENTURION PRO Silver Bullet (www.cprosolutions.com), the TWISTER T4 (www.twistertrimmer.com), the ULTRATRIMMER (www.ultratrimmer.com), the GreenBroz (www.greenbroz.com) and the THUNDERVAK Composter Plus. All are similar in operation—a rotating, reciprocating or stationary chamber containing the harvested cannabis stalks includes small slits or gaps in which—theoretically, but not in practice—only fan and sugar leaves (but not other parts of the plant) can slip easily, and behind each slit or gap is a mechanical cutting edge. The stalks are rotated or agitated inside the chamber, and with each cycle, the stalks come into contact with the slits, protruding leaves are sheared off, and the process repeats until complete. In practice, mechanical trimming with these machines results in over-trimming of the harvested stalk and significant damage to the flower and trichomes, which renders the most valuable parts of the plant useless and converted into waste.
For other agricultural applications, computer-controlled crop pickers, harvesters and trimmers have been created—for example, U.S. Pat. No. 9,226,446, to Moore (“Robotic Fruit Tree Pruner and Harvester Machine”) and U.S. Pat. Pub. No. 2011/0022231 to Walker et al. (“Apparatuses, Systems and Methods for Automated Crop Picking”). Both references disclose machine-vision systems coupled with computer-controlled mechanical armatures for pruning and harvesting fruit and other tree-borne crops. These devices, however, lack numerous features required or advantageous for the trimming of cannabis stalks, as described in greater detail below.
Specifically, the use of computer-vision for trimming plants and other agricultural products presents a unique challenge. In a typical computer-vision application, the central processor is programmed with instructions to search for and compare certain shapes, sizes and colors against a library of reference images, which permit the machine to “recognize” certain parts or features and act upon them. When working with plants and crops, however, reference images are far less useful because of wide variations in the natural shape, color and location of leaves, stalks, flowers, buds and other plant parts. Therefore, a different approach to computer-vision is beneficial.